Mike Hennessey has been sheriff of San Francisco for so long, and has done such a great job, that hardly anyone in town really thinks about the politics of the office any more. We take it for granted that we have the most progressive sheriff in the state, maybe the nation. We just assume that the jails will be run well, that the deputies will be held to a high standard of behavior, that alternatives to incarceration will be part of the program, that evictions will be handled in a humane way, that anti-recidivism programs will be funded and given priority, that immigrants won't face automatic deportation — and that San Francisco's top elected law-enforcement official will be a leader in innovative ways to approach law enforcement.

But it wasn't always that way, and it won't necessarily be that way in the future. This is a crucial election, pitting a progressive reformer who comes from the civilian world against two career law-enforcement officers. It's a chance to vote for someone who will continue Hennessey's legacy or to risk turning back the clock. That's why we're strongly endorsing Ross Mirkarimi, and only Ross Mirkarimi.

Hennessey was never a cop. He started off as a poverty lawyer, working in prison legal services under Dick Hongisto, who launched the tradition of progressive sheriffs in this city. He ran as a civilian and won — and there's a value to that. The Sheriff's Office in San Francisco has no Police Commission, no Office of Citizen Complaints; the only oversight of 850 sworn officers is the elected sheriff.

Since Hennessey's election, law enforcement lobbyists have managed to make changes in state law that bar anyone without formal police training from serving as a sheriff. Under current law, Mike Hennessey — who is widely respected by his peers — wouldn't be allowed to seek the office.

Mirkarimi meets the qualifications. He went through the San Francisco Police Academy as an investigator for the District Attorney's Office and graduated as president of his class. He holds the Peace Officers Standards and Training certificate and is thus in an unusual position: He can run for sheriff without being part of the law-enforcement fraternity.

It's not as if Mirkarimi is a stranger to the issues. He spent much of his first term in office working on public safety. When he took office in 2005, District Five, particularly the Western Addition, was plagued with violent crime. He personally appeared at every homicide scene, pushed for more police on the streets and for foot patrols and worked to organize the community around crime — and it worked. The murder rate dropped dramatically.

These days, Mirkarimi is working on anti-recidivism programs and wants to bring that approach to the office. Which is critical: Over the next two years, as the state implements a prison-system realignment, hundreds more inmates will be entering the San Francisco County Jail system — and while Hennessey has made a lot of progress, almost three quarters of the people who leave jail in San Francisco wind up getting in trouble with the law again.

The person who knows the job best is Hennessey — and he's made his position clear. When Hennessey decided three years ago that he was going to retire at the end of his term, he met with Mirkarimi and told him he'd like to see the supervisor as his successor. In fact, Hennessey told us, he offered to appoint Mirkarimi as undersheriff, so he could learn the job and run as the second-in-command. But that wasn't possible — city law prohibits sitting supervisors from taking another city job (unless it's an elected position).

If Hennessey had become acting mayor he would have appointed Mirkarimi sheriff. "Ross is the person I want to see in the job," Hennessey said. He noted two important reasons.